While working on my LR4 over the weekend, I discovered what I believe is a better way to tram along the Y axis – or at least, a better way to get very close to perfect without needing to resort to layers of tape. (Sorry, I didn’t think to take any pictures at the time, but they’re really not necessary…)
Remove the router and the top and bottom mounting rings. The face of the core where the rings attach should be exactly perpendicular to the surface of the spoilboard.
You’ll want to check at Xmin and Xmax - because it’s ridiculously easy to find you’ve mounted the gantry to the YZ plates with some twist in the gantry – one side might be nearly perfect when checking the tram; the other side can be way off. Or one side twisted forward and the other twisted back. And if you only check it in the middle of travel, well, you’ve got a partial solution that won’t be accurate at either end…
So move the core to Xmin, remove the mounting rings and check with a speed square (or something more precise if you have it). If the core isn’t perfectly square to the spoilboard, loosen the bolts that mount the gantry to the YZ plate, twist as needed to get to square and tighten the bolts. Double check that nothing moved; repeat if you need to.
Repeat the process at Xmax.
And finally, check it somewhere in the middle of X travel. If it’s off there (and it shouldn’t be), my suggestion is to loosen the top and bottom bolts on the X braces all the way across (except for the ends) and wiggle things to let the gantry find its own level. Re-check for square and you’ll probably find it’s pretty close. Snug the bolts up.
Now re-assemble the mounting rings and router, install your tramming tool and check. If it’s within maybe .5mm on a 3 or 4 inch tramming tool, you’re probably close enough. Feel free to chase zeros with some tape on the mounting rings if that’s not good enough for you.
This process doesn’t account for tramming along the X axis - I haven’t found that to be necessary, provided you’ve done a good job of leveling Z first. There’s really not much that can go out of whack along X, but if you find it’s not accurate, tape in the mounting rings is probably your best bet.